A jump server is a hardened and monitored device that spans two dissimilar security zones and provides a controlled means of access between them.
The jump server would span the two networks and typically be used in conjunction with a proxy service such as SOCKS to provide access from an administrative desktop to the managed device.
As SSH-based tunneling became common, jump servers became the de facto method of access.
Using SSH port forwarding or an SSH-based tunnel to the target host allows the use of insecure protocols to manage servers without creating special firewall rules or exposing the traffic on the inside network.
[10] In 2015, a compromised jump server allowed attackers access to over 21.5 million records in one of the largest breaches of government data in the history of the United States.